The invention relates to a pusher for scraper chain conveyors, especially of the kind used in underground mining. In particular, the present invention relates to a pusher with a bridge element that wraps over a lower portion of a scraper chain conveyor.
Pushers of this type used in underground mining usually comprise two parts, an upper and a lower part which are bolted together. The two parts secured firmly in place, anchor chain strands located within the jointing plane between the upper and lower parts of the pusher. For this purpose, each pusher is provided with chain beds for the chain links.
Pushers of this kind are known, for example, from the German patent application DE-A-27 17 449. The jointing plane between the upper and lower parts is configured such that the two ends of the lower part act as guide members. These two ends also engage the lateral guide profiles of the trough conveyor, while coupled to the upper part. This pusher design has become standard over the course of time because it offers enhanced wear resistance.
Although these pushers have by all means proved worthwhile in practice, the introduction of high forcesxe2x80x94for example as a consequence of strain introduced within the guide profilesxe2x80x94can cause them to bulge and distort, and, in particular, can cause the bolts to shear off and the upper part of the pusher to be severed off. This problem occurs most frequently after the chain exits large-diameter sprocket wheels of a kind commonly used. In this configuration, the chain strands with the scrapers mounted on them are diverted along a curved path by guide beads arranged in the conveyor frame. The curved path is used to permit the chain to bridge the difference between sprocket wheel and conveyor trough. The chains are guided downwards at a steep angle until they slide into the trough profile, with the scrapers taking up the necessary pressing force through end elements.
The object of the present invention is to overcome the drawbacks of the prior art, in particular by designing a pusher that is stable even when there is operating constraints. It is a further object that the pusher assembly be easily installed and maintained.
This object is established according to the invention by the features contained in the characterising part of claim 1, useful developments being characterised by the features contained in the subclaims.
According to the invention, the upper part of the pusher is designed as a bow-like bridge element, the ends of which wrap over the two ends of the lower part from above and confine the lower part in a clasp-like manner. In cases of strain on the pushers within the lateral guide profiles of the trough conveyor, which occurs especially during the transition from sprocket wheel to conveyor trough, the forces generated are introduced predominantly in the region of the wrap-over ends. However, because the ends of the upper part embrace the lower part in a clasp-like manner, distortion of the upper and lower parts is prevented. This arrangement provides an advantage over the prior art because it avoids severing a pusher part. This design also considerably facilitates assembly, because the lower part, being of smaller width (transverse to the direction of transport) than the upper part, can very easily be pushed under the two chain strands when the pusher is being fitted. The bridge-like upper part is then simply mounted on top and bolted. If, in addition, as is expedient, the upper and lower parts are symmetric with respect to the transverse center line, i.e. the line perpendicular to the longitudinal direction of transport and axis/axes of the chain strand or strands, assembly becomes even easier because the pushers can also be fitted laterally transposed. When fitting the pushers, it is no longer necessary to differentiate between the front and rear ends of the pusher in terms of the direction of transport.
The lower part is preferably confined in clasp-like manner within the space delimited by the bridge-like upper part. This structure results in a stable joint between the upper and lower parts. In this connection, it is expedient to have a small space between the upper and lower parts in the area of the central jointing plane, because this permits desirable pretensioning between the upper and lower parts by means of the bolts. It is especially beneficial if this space is effected by way of the distal cuneiform contact surfacesxe2x80x94which run obliquely outwards from top to bottomxe2x80x94between the wrap-over ends of the upper part and the ends of the lower part.
It is furthermore of advantage to design the guide surfaces of the upper part so that the preferably cuneiform ends of the bridge-like upper part are guided within the lateral guide profiles of the trough conveyor. Most of the wear on the parts then occurs in the upper part, which is very easily removed for repair purposes and can be replaced by a repaired upper part.
By means of appropriate recesses in the area of the upper port guide surfaces, raised wear surfaces are obtained that can be repaired very easily by build-up welding or by welding on shells. A check for the occurrence of wear can be provided by wear marksxe2x80x94grooves, flutes or stepsxe2x80x94in these upper wear surfaces. If the grooves, flutes or steps are no longer visible, the pusher can be considered worn to the extent that the need for maintenance to replace or repair the scraper is easily observed.
Again in the context of wear markings, the invention provides that each chain bedxe2x80x94formed by two axial chain conduitsxe2x80x94features a peripheral, groove-like depression. These depressions serve simultaneously as wear marks and to accommodate the weld of the chain links. As a result, the chain links are accommodated with very little friction, in particular, both positively and non-positively in the pushers.
Another useful feature of the invention is that to reduce friction, the ends of the lower part are recessed, creating a free space which bridges the welds formed by welding the base plate to the lateral guide profiles of the trough conveyor. It is to advantage if the recessed surfaces are flush with the lower surface of the wrap-over ends of the upper part.
It is additionally expedient to provide a groove-like recess in the top surface of the upper part, the recess running transversely with respect to the direction of transport and preferably extending from the bridge centre to the proximity of the holes for the bolts. This measure not only saves material, but also gives the upper part an essentially T-shaped cross-section, as a result of which the moment of resistance in the direction of transport is increased.
Another feature permitting high stresses to be taken up in the direction of transport is the provision of centring noses or centring projections in the region of the ends of the lower part and the lands between chain conduits. These projections prevent conveying forces from causing displacement of the upper and lower parts.